Conventionally, semiconductor wafers are coated with photoresist material and exposed to radiation from a mercury lamp in order to apply electrical circuits thereon. This process is repeated a number of times, typically in a projection mask alignment and exposure system. It is extremely important that a wafer be precisely oriented for each exposure in order to insure correct registration of each successive image. The usual methods of transporting a wafer within such a system have been by means of belts and air tracks. However, these methods have not provided sufficiently positive control. As a result, wafers have tended to slide and bounce, thereby generating particles which, upon landing on the wafer, would damage the micro circuits being printed.
Accordingly, it is an object of this invention to increase the control exercised over each wafer while, at the same time, precisely aligning each wafer with a minimum of handling. The manner in which this is achieved will be apparent from the following description and appended claims.